1. There were definitely some issues with binding to cores and process layouts on Opterons that should be fixed in the 1.5.5 that was finally released today.

2. It is strange that the performance of barrier is so much different between 1.5.4 and 1.5.5. Is there a reason you were choosing different algorithm numbers between the two? (one of your command lines had "coll_tuned_barrier_algorithm 1", the other had "coll_tuned_barrier_algorithm 3").